Agitator member for a magnetic agitator



May 26, 1970 F. VOGTLE ET AL 3,514,214

AGITATOR MEMBER FOR A MAGNETIC AGITATOR Filed March 1, 1968 FIG-4 FIG-5 FIG-6 FIG-7 FIG-8 FIG-9 FIG-IO IN VENTORS 7 /22 /a'7// United States Patent 3,514,214 AGITATOR MEMBER FOR A MAGNETIC AGITATOR Fritz Vogtle, 88 Winkelhofer Strasse, 7930 Ehingen (Danube), Germany, and Wilhelm Schmitt, Chemisches Institut, 6900 Heidelberg, Germany Filed Mar. 1, 1968, Ser. No. 709,694 Claims priority, application Germany, Mar. 2, 1967, V 33,124 Int. Cl. B01f 7/16 US. Cl. 416-3 24 Claims ABSTRACT OF THE DISCLOSURE An agitating member adapted to be rotated and guided by magnetic forces, which includes rod means and also includes flow resistance increasing means, for instance disc means, extending from said rod means in the radial direction thereof and increasing the flow resistance of said rod means in the longitudinal direction thereof.

The present invention concerns an agitator part for a magnetic agitator in which the agitator part has the form of an agitating rod which is freely movably located in the container for receiving the medium to be agitated and which is rotatable by magnetic power transfer.

Magnetic agitators of the above mentioned type are used in laboratories and also in the chemical industry, particularly in connection with processes according to which reactions are to take place in vacuum or under the exclusion of air, and in which additionally an agitating or st1rring of the medium is desired.

It has been proved that magnetic agitators of the above mentioned type, particularly in the above mentioned instances, have an advantage over mechanical agitators for similar purposes since mechanical agitators have to be built up of precision elements, and furthermore, when assembling such mechanical agitators great care has to be taken, While on the other hand, still no service and disturbance free operation can be assured because in View of the frequently extreme working conditions, a sticking or jamming of the agitator shaft can never be safely e tcluded. Over such mechanical agitating devices, magnetic agitators excel by their simplicity of construction and the low cost of construction. However, the heretofore known magnetic agitators are not fully satisfactory as to their working method and construction. This is due to the fact that with the free rotational movement of the agitating rod, the safe central guiding in the agitating vessel is not always assured with a glass cup or ball-shaped vessel.

The agitating rod is generally sufficiently precisely centered by the field of forces of the magnet which rotates outside the vessel. This centering operation has, however, proved not sufiiciently strong to assure that, when the agitating rod falls out of step with the driving magnet, a movement of the agitating rod from its central position in the direction of its longitudinal axis will be safely prevented. Such falling out of step may occur in view of more or less suddenly changing loads acting on the agitating rod. Inasmuch as load variations in the torque to be produced by the agitating rod and sufficient for the falling out of step of the agitating rod can be produced already by a change in the speed of the driving magnet, a compacting of the medium to be agitated, for instance, during a chemical reaction, or as a result of a change in the flow conditions, and since an agitating rod which has moved out of its central position can practically no longer be returned to its central position when the agitating process continues and thus will be thrown around in the vessel at random, heretofore, magnetic agitators were 3,514,214 Patented May 26, 1970 ice limited to low rotational speeds in order to avoid damage or destruction to the agitating vessels. In addition to higher rotational speeds which were dangerous since with increasing speed of the agitating rod also the danger of falling out of step greatly increased, the employment of larger and heavier agitating rods necessary for greater agitating effects were heretofore not recommended, since, of course, with a falling out of step of such heavy agitating rods, the danger of destruction and damage to the vessel was much higher than with small heretofore customary agitating rods.

It is, therefore, an object of the present invention to improve the heretofore known magnetic agitators so that also greater and heavier agitating rods with a corresponding higher agitating output will be possible.

It is another object of this invention to provide a magnetic agitator, as set forth in the preceding paragraph, which will assure that, even when a falling out of step of the agitating rod occurs, a destruction of, or damage to the agitating vessel will not occur.

These and other objects and advantages of the invention will appear more clearly from the following specificaltiog in connection with the accompanying drawings, in w 1c FIG. 1 diagrammatically illustrates a magnetic agitating rod with a plurality of stabilizing discs thereon.

FIG. 2 illustrates a method of connecting a stabilizing disc to the rod.

FIG. 3 is a side view of a stabilizing disc as used in FIGS. 1 and 2.

FIGS. 4 and 5 respectively illustrate two ways of connecting stabilizing discs to magnetic agitating rods.

FIGS. 6-10 respectively illustrate various designs of stabilizing discs.

FIGS. 11 and 12 respectively illustrate two different forms of magnetic agitating rods with stabilizing discs designed in conformity with a most favorable flow.

FIG. 13 is a side view of a stabilizing disc according to FIG. 11.

FIG. 14 is a still further embodiment of an agitating rod according to the invention.

The objects outlined above have been realized by the fact that the agitating member in the form of an agitating bar comprises an enlargement which increases its flow resistance in its longitudinal direction. Such a design of the agitating bar will in a twofold manner contribute to the stabilization of the movement of the agitating rod during the agitating operation. More specifically, on one hand, in particular each accelerated displacement of the agitating rod in its longitudinal direction as it may be caused by a falling out of step of the agitating rod will very soon be braked so that the deviation of the agitating rod from the center is small, and that the agitating rod can, in view of the magnetic field guiding said rod be caught again and rotated much easier. On the other hand, a corresponding design of the sections or par s of the agitating rod which increase the flow resistance will be able to bring about that the agitating rod, when falling out of step will substantially not be able to displace itself radially outwardly. Instead, these displacing movements will be converted to a movement in the circumferential direction, preferably in the direction of rotation. Such a designed agitating rod is self-centering to a great extent so that the employment of heavy agitating rods, and in particular the employment of higher agitating speeds will now be possible.

The improved agitating effect, due to the employment of higher speeds will be felt in particular with high viscous liquids, such as oils with which a higher agitating resitance is encountered in conformity with the higher viscosity, and in which due to the higher agitating resistance, a lateral shearing out occurs as it is encountered with heretofore known magnetic agitators at even low speeds which were not suificient for a proper agitating effect. The flow resistance of the agitating rod may within the framework of the invention be increased by at least one disc, or the like, extending transverse to the longitudinal direction of the rod. Preferably, at least near to the two ends of the rod, there is provided one disc each. Such a design makes it possible so to improve the heretofore employed magnetic agitating rods that they can also be used in connection with the present invention.

For purposes of obtaining a simple cleaning of the agitating rods and in order to be able easily to exchange the discs for adapting the same to the respective medium to be processed, it may be advantageous to mount the discs detachably. To this end, the discs may be held by clamps, for instance, by spring rings or the like which are advantageously coated with an elastic protective coat. If desired, the disc may also be connected to the respective agitating rod by a thread, especially a conically designed thread, but self-securing connections are preferred.

When the agitating rod is made of a single piece and of a shape advantageous for the purpose according to the invention, it may be covered as an entirety by a protective coat, for instance, of ceramic, non-magnetic metal, synthetic material such as a polyamide, or rubber. When an agitating rod is employed in the form of a smooth rod which likewise may be provided with a coat, the discs may be made of a material which is insoluble in the respective medium to be agitated. As materials in this connection, ceramic materials, non-magnetic metals, synthetic materials, as for instance, polyamide, or rubber may be used.

If desired, the disc may be produced from a magnetic material in which instance it is then advisable to cover the same with a coat which is insoluble in the medium to be agitated. The same principle also applies to the agitating rod, in which instance the coating material may at the Same time serve as means for holding the discs on the rod.

Within the framework of the present invention it may also be advantageous to arrange at least one of the discs on the agitating rod so that it can turn thereon. Such a feature is particularly expedient in heavy operation because it has been found that magnetic agitating rods with discs fixed at their ends do not rotate about their own longitudinal axis in operation, but drag on the bottom of the vessel. This dragging movement can be avoided by the provision of rotatable discs so that the discs are able to roll on the vessel bottom in counter current directtion. In order to be able by means of said discs, in addition to a rotation of the medium to be agitated, also to obtain turbulence of said medium, it may be advantageous to provide the discs with an irregular circumferential shape. The discs may for this purpose be designed, for instance, as polygons, or their circumference may have notches, profiles, teeth, or the like. If a rolling of the disc is desired, the disc must, of course, be circular.

If the magnet eifecting the drive is arranged below the vessel, it is expedient to locate the agitating rod as close as possible to the bottom because the force of the magnetic field decreases with increasing distance. For this reason it may be advantageous to design the discs so that they are unilaterally flattened close to the insert opening of the agitating rod so that the latter will be very close to the bottom.

The same effect can be realized by means of discs which near the circumference thereof, are provided with bores for receiving the agitating rod. If these bores have different diameters or are of different shape, there also exists the possibility to employ the same discs for agitating rods of different sizes. In order not unnecessarily to increase the agitating resistance by the discs, it may be i 4 expedient to design the disc streamlined. This is particularly successfully possible with discs which have a steady location with regard to the bottom of the vessel. To this end, the disc may be arched outwardly, for instance, in conformity with the radius of curvature or may be of a drop-shaped design.

A particularly economical design will be obtained according to the present invention by forming the cover or coat for the agitating rod consisting of magnetic material by a hose which may be of polyamide. Such coated agitating rod can be connected to the disc-shaped member without welding, cementing, or the like, of the hose ends if said disc-shaped member is provided with a blind hole for receiving the agitating rod. Advantageously, the blind hole may be provided with a thread or grooves, and the tight connection may furthermore be improved by shrinking so that a welding or bracing between the coating material and the discs will not be necessary. The end of the hose extends in conformity with the invention somewhat beyond the end of the rod so that the agitating rod can, together with the hose, be easily introduced into the blind hole in such a manner that the thread grasps the hose without the necessity of providing said hose with a thread or with a fully cutout thread or grooves. By threadedly connecting the threadless or not fully cutout thread of the hose together with the disc, an absolutely tight connection of the hose end in the blind hole is obtained because the thread of the blind hole presses itself into the hole.

A further advantageous embodiment of the invention will be obtained by providing each agitating rod end or each disc with a safety device in the form of a spring ring or spring disc which will prevent the disc from loosening itself or turning itself out.

Another embodiment which is particularly advantageous from the production standpoint inasmuch as no previous machining of the portions of the hose-shaped cove? and the disc to be connected thereto is necessary, will be obtained by connecting the hose by friction welding with the disc-shaped part.

Referring now to the drawing in detail, FIG. 1 shows a magnetic agitating rod with three stabilizing discs 2-4 mounted thereon. The magnetic agitating rod 1 may be of the heretofore customary type which, however, is, in conformity with the present invention provided with stabilizing discs shown in the drawing. The mounting of such stabilizing discs on the agitating rod 1 may be effected in any convenient manner. In this way it is possible by means of such stabilizing discs to so convert heretofore known agitating rods that the advantages according to the invention can be realized and also particular circumstances can be taken care of.

Fundamentally, the diameter of the discs may be selected at will. Frequently, however, the diameter is limited, due to the fact that the agitation takes place in pistons with a neck connected thereto. In case stiff discs are to be employed, the diameter of the discs must, of course, not exceed the neck diameter of the vessel. Diameters of from 20 to 25 millimeters for the discs have frequently proved sufficient and are generally advantageous because they still permit the employment of magnetic agitating rods with a diameter up to approximately 8 millimeters.

According to the arrangement of FIG. 1, there is, in addition to the stabilizing discs 2, 4 located at the ends of agitating rod 1, also provided a disc 3 which is arranged approximately halfway between the ends of the agitating rod. The additional disc 3 yields primarily an increased turbulence of the material to be agitated. For this reason, it may be advantageous to shape disc 3 somewhat differently and to give it a different size with regard to the end discs 2, 4.

FIG. 2 illustrates possibilities of connecting the stabilizing disc 5 to an agitating rod 1'. As will be seen from the drawing, near the end of rod 1' there is a neck 6 upon which a disc 5 may be pressed, if a disc of elastic material is to be used. The other end of agitating rod 1 is provided with a stud 7 having a bore 8 therethrongh so that a disc 5 placed upon said stud 7 may be secured thereto by means of a cotter pin or the like. Similar to the discs which, for instance, may consist of a synthetic material which will not dissolve in the medium to be agitated, also the pin to be passed through bore 8 may consist of such synthetic material.

FIG. 4 shows the connection of discs 5, 5 on an agitating rod 1 of customary design. In this instance, clamping rings 9 are employed which are adapted to be mounted on the agitating rod and which similar to the disc 5 may engage an inner groove 10 of the disc or which may be arranged on both sides of the disc 5.

FIG. 5 shows an embodiment according to which the agitating rod 1 is eccentrically arranged or passed through the stabilizing discs 10, 11. A disc design suitable for this arrangement is shown by way of example in FIG. 6. According to FIG. 6, the disc 12 is provided with a flattened engaging surface 13 while the remaining portion is circular. Disc 12 has a central bore 14 and additional bores 15 which may be of different sizes so that there is afforded the possibility of placing the disc 12 on agitating rods 1, of different diameters. In such an instance, however, the effect of the particular closeness to the bottom of the agitating rod when the flattened surface 13 of the disc 12 engages the bottom, will be lost. The discs 10' and 11 according to FIG. 5 may, as to design, correspond to the disc 12 of FIG. 6. In connection with the disc 10 there is furthermore indicated the possibility of assuring a particularly good fit of the disc on an agitating rod with a smooth surface. In this instance, a spring ring 16 is pressed into the disc so that a particularly strong clamping engagement is assured.

FIGS. 7-l0 illustrate a plurality of different stabilizing discs. The circular disc 17 of FIG. 7 has only a central bore 14, and having plane lateral surfaces 18, thus represents an embodiment which can be cut off in a particularly simple manner directly from stock material. According to the embodiment of FIG. 8, the stabilizing disc 19 is provided with a central bore while its circumference is provided with recesses 20. These recesses may be of different shapes and depending on the frequency and shape thereof will, in addition to the agitating effect, also bring about an increased turbulence in the medium to be processed. The disc 21 according to FIG. 9 is polygonal and is advantageous in all instances in which a plurality of discs 21 is non-rotatably connected to an agitating rod, and in which a rotation of the agitating rod about its longitudinal axis is desired. It will be appreciated that when the individual discs 21 are offset with regard to each other, no stable location or position for the agitating rod is obtained and the agitating rod will, during the agitating operation, rotate more or less disquietly whereby the general agitating effect will be improved.

FIG. 10 shows a disc 22 which has a plurality of bores 23 along a circle. The bores 23 are all eccentrically located so that a relatively short distance of the agitating rod from the vessel bottom is obtained. The said bores 23 furthermore have different diameters so that they can be employed for agitating rods of different thickness.

FIGS. 11 to 13 illustrate various embodiments of discs which have a particularly low flow resistance in the direction of rotation. According to FIG. 11, the agitating rod 1 is provided with tear-shaped stabilizing discs 24 which may be fixedly connected to the agitating rod. This design will in the direction of rotation yield a low flow resistance of the stabilizing discs and when the agitating rod is eccentrically located may bring about that the ac celerations in the longitudinal direction of the rod, as they occur when the agitating rod gets out of step with the driving magnet after losing its centering position, are converted into accelerations in the direction of rotation. In this way, it is possible even Within a shorter time to catch the outof-step agitating rod.

The stabilizing discs 25 and 26 in FIG. 12 represent some modifications with regard to the stabilizing discs of FIG. 11. The stabilizing disc 25 is arched similar to the stablizing disc 24, but avoids the tear-shape which requires somewhat more complicated manufacturing steps. The disc 26 has a simple mushroom shape. Even though the discs 25 and 26 have a somewhat simple design they can produce a similar effect as disc 24.

If, with the discs designed in a streamlined manner a short distance is desired between the agitating rod and the engaging surface of the discs, a design according to FIG. 13 may be selected. Disc 27 shown in FIG. 13 is somewhat elliptical when seen from the side so that the distance of the agitating rod from the engaging surface is comparatively short.

FIG. 14 shows an agitating rod 1 having a hose thereon forming the coating for the rod. The said hose may be of polyamide and is inserted into a blind hole in disc 28.

When the connection between discs and the hose-covered agitating rod is established by friction welding, the hose 30 may be welded to a depression of the disc or may be welded plane thereto. If desired, the blind hole 29 may be provided with a thread or groove for engagement with the respective hose end. According to FIG. 14, hose 30 slightly protrudes beyond the ends of the rod 1.

It is, of course, to be understood that the present invention is, by no means, limited to the particular embodiments illustrated in the drawing, but also comprises any modifications within the scope of the invention.

What we claim is:

1. An agitating member adapted to be rotated and guided by magnetic forces, which includes: rod means, and flow resistance increasing means extending from said rod means in the radial direction thereof for self centering and increasing the flow resistance against shift of said rod means in the longitudinal direction thereof.

2. An agitating member according to claim 1, in which said flow resistance increasing means comprise considerably greater than rod diameter disc means mounted on said rod means.

3. An agitating member according to claim 2, in which at least two disc means of approximately thrice rod diameter are provided on said rod means and are respectively mounted near the end portions thereof.

4. An agitating member adapted to be rotated an guided by magnetic forces, which includes: rod means, and flow resistance increasing means extending from said rod means in the radial direction thereof and increasing the flow resistance of said rod means in the longitudinal direction thereof, said flow resistance increasing means comprising disc means mounted on said rod means, and spring ring means securing said disc means in position and being covered with a coatt of a material non-soluble in the medium to be agitated by said agitating member.

5. An agitating member according to claim 2, in which both said rod means and said disc means thereon have at least their surfaces formed by a material which is nonsoluble in the medium to be agitated by the agitating member. I

6. An agitating member according to claim 5, in which said material comprises at least one of the substances selected from the group consisting of ceramics, glass, non-magnetic metals, polyamide, and rubber material.

7. An agitating member according to claim 2, in which said disc means are covered by a coat of a material which is non-soluble in the medium to be agitated by said rod means, said coat firmly connecting said disc means peripherally to said rod means.

8. An agitating member adapted to be rotated and guided by magnetic forces, which includes: rod means, and flow resistance increasing means extending from said rod means in the radial direction thereof and increasing the flow resistance of said rod means in the longitudinal 7 direction thereof, said flow resistance increasing means comprising disc means mounted on said rod means, at least one of said'disc means being rotatably secured on said rod means.

9. An agitating member according to claim 2, in which said disc means have an irregular circumferential contour.

10. An agitating member according to claim 2, in which said disc means have a polygonal circumferential contour.

11. An agitating member according to claim 2, in which said disc means have a plurality of bores therethrough of different diameters.

12. An agitating member according to claim 9, in which said disc means have a circular outer contour limited by a chord.

13. An agitating member according to claim 9, in which said disc means has an outer serrated contour.

14. An agitating member according to claim 2, in which said disc means are eccentrically arranged on said rod means.

15. An agitating member adapted to be rotated and guided by magnetic forces, which includes: rod means, and flow resistance increasing means extending from said rod means in the radial direction thereof and increas ing the flow resistance of said rod means in the longitudinal direction thereof, said flow resistance increasing means comprising disc means mounted on said rod means, said disc means having a stream-lined cross sectional contour.

16. An agitating member adapted to be rotated and guided by magnetic forces, which includes: rod means, and flow resistance increasing means extending from said rod means in the radial direction thereof and increasing the flow resistance of said rod means in the longitudinal direction thereof, said flow resistance increasing means comprising disc means mounted on said rod means, the outwardly facing end face of said disc means being curved outwardly.

17. An agitating member according to claim 1, in which a hose is placed peripherally over said rod means and forms a protective coat therefor.

18. An agitating member according to claim 17, in which said peripheral hose is of polyamide.

19. An agitating member adapted to be rotated and guided by magnetic forces, which includes: rod means, and flow resistance increasing means extending from said rod means in the radial direction thereof and increasing the flow resistance of said rod means'in the longitudinal 8 direction thereof, a hose placed over said rod means and forming a protective coat therefor, that side of said disc means which faces away from the outside being provided with a blind hole receiving the respective adjacent end of said hose.

20. An agitating member according to claim 19, in which of the two interengaging portions respectively pertaining to said blind hole and said hose at least the inner wall of said blind hole is provided with a thread.

21. An agitating member according to claim 17, in which said peripheral hose slightly protrudes beyond the outer ends of said rod means.

22. An agitating member adapted to be rotated and guided by magnetic forces, which includes: rod means, and flow resistance increasing means extending from said rod means in the radial direction thereof and increasing the flow resistance of said rod means in the longintudinal direction thereof, and a hose placed over said rod means and forming a protective'coat therefor, said hose being friction-welded to said disc means.

23. An agitating member for a magnetic stirrer, comprising: a rod means, means enveloping said rod means, circular-formed disc means permanently secured transversely with respect to said enveloped rod means and having a diameter substantially greater than that of said enveloped rod means, said disc means having a flow propitious cross section.

24. An agitating member for a magnetic stirrer, comprising: a rod means, a polyamide hose enveloping said rod means, circular-formed polyamide disc means secured to said rod means around said polyamide hose trans versely of longitudinal direction of said rod means, said polyamide disc means having an outer diameter substantially greater than said enveloping polyamide hose and having aperturing complementary thereto for receiving said polyamide hose, and a frictional weld juncture peripherally inside aperturing of said disc means held thereby to said corresponding polyamide hose in mating relationship.

References Cited UNITED STATES PATENTS 2,562,714 7/1951 Hawtof 259l44 2,641,452 6/1953 Wagner 259-144 X 2,951,689 9/1960 Asp et al 259-144 WILLIAM I. PRICE, Primary Examiner 

